1. Field of the Invention
The present invention relates to a liquid crystal display device and particularly to an improvement in the control lines that controls an analog switch circuit in the liquid crystal display device having a system of apportioning to a plurality of signal lines video signals supplied from video signal lines.
2. Description of the Prior Art
In recent years, liquid crystal display devices having features of light weight, small thickness and small power consumption have widely been used as liquid crystal display devices for information equipment, such as personal computers and word processors, and for video equipment, such as television sets, video cameras, digital cameras and car navigation systems. A liquid crystal display device has a liquid crystal display panel having liquid crystal materials sealed between two substrates (an array substrate and a counter electrode) and, in the liquid crystal display panel, a voltage on-off operation controls the orientation of the liquid crystal materials a transmitted light on-off operation performs an image display.
In the liquid crystal display panel, as means for supplying a power source and control signals for a scan line driving circuit, a power source for the counter electrode and a power source connected to an auxiliary capacitor, a flexible wiring substrate having mounted thereon a drive IC for supplying video signals has been utilized. In this case, the above power sources and control signals are supplied generally not via the drive IC, but using the opposite end portions of the flexible wiring substrate without use of the wiring portion for supplying the video signals.
On the other hand, in recent years, a signal line driving system has been proposed, in which an analog switch circuit is formed on an array substrate constituting a liquid crystal display panel, the ratio of the number of video signal lines from a drive IC and the number of signal lines on the array substrate is set to be 1:2, and one of the two type of signal lines is selected using the analog switch circuit to supply the video signal, whereby it is made possible to reduce the number of the drive IC. In a liquid crystal display panel especially using a polysilicon thin film transistor, this signal line driving system is easy to adopt. Incidentally, the ratio of 1:2 of the number of the video signal lines and the number of the signal lines on the array substrate is not limitative. The ratios of 1:3 and 1:4 are possible.
In the signal line driving system, it is necessary to supply the power sources and control signals to the analog switch circuit on the array substrate. The control lines for supplying the power sources and control signals are also wired toward the opposite end portions of the flexible wiring substrate having the drive IC mounted thereon (refer, for example, to JP-A 2003-270660).
The liquid crystal display device disclosed in the prior art JP-A 2003-270660 is provided with a liquid crystal display panel and a drive circuit for supplying video signals to video signal lines formed on the liquid crystal display panel. The drive circuit comprises a first drive circuit formed by the same process as pixels provided on the liquid crystal display panel and a second drive circuit connected to the liquid crystal display panel formed. The first drive circuit is constituted by a switching circuit capable of allocating outputs of the second drive circuit to a plurality of video signal lines. The prior art JP-A 2003-270660 discloses in FIG. 8 or 9 an example of forming on the opposite end portions allocation control signal lines for driving the switching circuit.
In recent years, the number used per panel of a drive IC used for a liquid crystal display device has been directed to reduction and moreover the aspect ratio of display panel has been shift from 4:3 to 16:9. In this case, when a division control signal lines for supplying the power sources and control signals to the switching circuit is pulled along from the opposite end portions of the flexible wiring substrate having the drive IC mounted thereon, the wiring length on the array substrate becomes long to possibly entail a problem of the voltage depression owing to interconnection resistance, the delay signals, and attenuation of the control signals.
Particularly in the case of forming the analog switch circuit on the array substrate and performing a signal line selection drive method that switches signal lines for supplying the video signals, based clock frequency is high and easy to make noise, and the delay signals and attenuation of the signals possibly affects greatly the quality of images to be displayed on the liquid crystal display panel.
The present invention has been proposed in view of the conventional actual situation, and the object thereof is to provide a liquid crystal display device capable of suppressing the wiring length of control signal lines for supplying power sources or control signals to an analog switch circuit to the minimum and suppressing the deterioration of an image quality resulting from the voltage dropping, the signal delay, and the control signal attenuation.